100A DP Isolator Installation Between Meter and CU

[jaydub]

Hi guys,

When installing a new CU does anyone ever install a 100A double pole isolator switch between the meter and the consumer unit?

Very often I come across 16mm tails which need to be upgraded to 25mm so I join the old tails to new in a Henley block and get the DNO to come and upgrade their side at their convenience.

Instead of using a henley block could I use an isolator instead?

In anyones opinion would there be any disadvantages to this?

I wouldhave thought having an isolator would be very handy but the meter guys hardly ever bother putting one in, even now.

They're also relatively inexpensive. Another thing, I cannot seem to finda 2-module metal enclosure so would this would be okay in a plastic enclosure? That to me seems like a bit of grey area.

Any help appreciated. Thanks

 

[Midwest]

So what they are saying is, if you choose to install an isolator you should carry out a risk assessment to cover your own --- in case it catches on fire through fault or negligence. That is what it sounds like to me...?

IMO I can rarely see the time when 'I' would install an isolator. I can see the occasion when I would install a switch fuse isolator, in which case I would install a metal one.

However, the other consideration is, would the DNO/Supplier allow you to fit a metal enclosure in 'their' meter cabinet?

 

[Midwest]

Why would you use a 25mm earthing conductor in domestic?
25mm 2 core swa or 16mm for the line and neutral and a separate 16mm earthing conductor ran in parallel surely?

I probably go for a 25mm 3c myself, mostly if it weren't too long. Installing one thing instead of two things. But then I'm lazy.

 

[Ian1981]

IMO I can rarely see the time when 'I' would install an isolator. I can see the occasion when I would install a switch fuse isolator, in which case I would install a metal one.

However, the other consideration is, would the DNO/Supplier allow you to fit a metal enclosure in 'their' meter cabinet?

To be honest I can’t see you fitting one in their meter box as you just don’t have the room.
It’s hard work trying to convince a builder to fit a 2nd meter box to house the fused isolator

 

[multimick]

Why would you use a 25mm earthing conductor in domestic?
25mm 2 core swa or 16mm for the line and neutral and a separate 16mm earthing conductor ran in parallel surely?

yeah i ran 25mm 3 core it was only 10 meteres

 

[jaydub]

Crikey this really is minefield of what if's isn't it...

Maybe I will not bother with it...

 

[Ian1981]

yeah i ran 25mm 3 core it was only 10 meteres

You can get a reducer pin for the 25mm so you can terminate into the terminal easier.

 

[multimick]

Crikey this really is minefield of what if's isn't it...

Maybe I will not bother with it...

just getting my post count up

 

[Midwest]

To be honest I can’t see you fitting one in their meter box as you just don’t have the room.
It’s hard work trying to convince a builder to fit a 2nd meter box to house the fused isolator

I did come close to fitting one in a cabinet on one job. Was room just. Got to the point of enquiring with the DNO, but when I measured my tails run, it was 3m.

 

[Midwest]

just getting my post count up

Ask that Chinese chick to add you to her spybot list, that will ramp things up for you.

 

[Ian1981]

I did come close to fitting one in a cabinet on one job. Was room just. Got to the point of enquiring with the DNO, but when I measured my tails run, it was 3m.

My experience regarding the length of the ‘tails’ with the DNO is basically “we don’t care”

 

[Midwest]

My experience regarding the length of the ‘tails’ with the DNO is basically “we don’t care”

I'm shocked. I'm always very careful measuring the run of the tails. Fingertip to opposite --- (1metre).

 

[Octopus]

Murdoch, does it not specify in BS7671 that all supplies must now be 25mm regardless?

No - but the "pretty" pictures in the OSG do suggest this is the case.

When I do a CU change I carry 25mm tails, 16mm GY and 10mm GY and the appropriate Henley blocks and MET's - then I can cover each eventuality....

If its a new build I certainly would fit 25mm tails.

 

[mhar]

The alternative to 'upgrading' the tails to 25mm is to ensure that the fuse does not exceed 80A.
What supply do people think they get these days? Halfway down this page Western Power Distribution - Information for electrical installers - https://www.westernpower.co.uk/Connections/Information-for-Electrical-Installers.aspx is the specification for a standard WPD supply (albeit one that needs one letter inserting).
Does the size of the supply vary accross dnos?

 

[Percyprod]

Working for dno, meter tails governed by rating of cu, NOT supply fuse. 100amp cu=25mm tails.

 

[static zap]

.......careful measuring the run of the tails. Fingertip to opposite --- (1metre).

May have to re-calibrate for "Moob-droop" !